The present invention relates to an electric insulator for the interior of an encapsulated electric device in which electric discharges and/or arcs occur at least at times and which is filled with an electronegative gas, said insulator comprising at least one carrier reaction resin hardenable by polymerization and at least one filler.
It is known to produce such electric insulators for electric devices using a casing resin with a filler capable of resisting not only the decomposition products of the electronegative gas which form due to electric discharges and/or arcs but also the compounds which form due to the reaction of said decomposition products with other chemical elements contained in the encapsulation. The most preferred filler for such casting resin insulators is aluminum oxide, particuarly in the form of molten corundum. A disadvantage of these insulators made of hardened casting resin and molten corundum is that, relative to the carrier resin, the filler is so heavy that sedimentation problems are encountered in production, and the final insulators are relatively heavy. The hardened insulators always require finishing, an operation which can only be performed with expensive diamond tools. Another disadvantage is that, for economic reasons, corundum cannot be used in chemically pure form, and the impurities of the corundum have a detrimental effect on the electrical strength of the insulators.
Insulators produced of pure resin without filler have the disadvantage of shrinking too much while making it impossible to produce castings which are true to shape.